A known variable valve timing control apparatus for controlling a relative rotation phase of a driven-side rotation member relative to a driving-side rotation member that rotates in synchronization with a crankshaft of an internal combustion engine may include an intermediate lock mechanism. The intermediate lock mechanism is configured to lock the aforementioned relative rotation phase at an intermediate phase positioned in a range between a most retarded angle phase and a most advanced angle phase (i.e., the intermediate lock mechanism is in a locked state). Such variable valve timing control apparatus is disclosed in JP2011-256772A which will be hereinafter referred to as Reference 1. The variable valve timing control apparatus disclosed in Reference 1 includes the driven-side rotation member arranged to be coaxial with the driving-side rotation member and integrally rotating with a camshaft for opening and closing a valve of the internal combustion engine, fluid chambers defined between the driving-side rotation member and the driven-side rotation member, and partition portions provided at the driven-side rotation member, each of the partition portions dividing each of the fluid chambers into an advanced angle chamber and a retarded angle chamber. The driving-side rotation member is disposed to be sandwiched between a plate-formed sprocket and a plate-formed cover and tightened by bolts.
At a time when the engine is started or the engine is restarted from a failure state including an engine stall, for example, the intermediate lock mechanism may be in an unlocked state in which the locked state is released so that each of the partition portions is positioned in the vicinity of the most retarded angle phase or the most advanced angle phase. At this time, because the engine is started after once the engine is stopped, almost no oil exists in the fluid chambers. As a result, the camshaft repeatedly rotates in an advanced angle direction and a retarded angle direction by receiving a reaction force from an intake valve or an exhaust valve, which causes the partition portions provided at the driven-side rotation member to repeatedly and strongly make contact with side walls of the fluid chambers. A contact position between each of the partition portions and the side wall of each of the fluid chambers may be thus fluctuated, which may cause the most retarded angle phase and the most advanced angle phase to deviate from original phases that are specified beforehand.
Therefore, according to Reference 1, in order to avoid direct contact between the partition portions and the side walls of the fluid chambers, a first protrusion portion that protrudes in the retarded angle direction is formed at one of the partition portions while a second protrusion portion that protrudes in the advanced angle direction is formed at another one of the partition portions. In a case where the relative rotation phase reaches the most retarded angle phase, the first protrusion portion makes contact with one of the bolt while, in a case where the relative rotation phase reaches the most advanced angle phase, the second protrusion portion makes contact with another one of the bolts.
According to the aforementioned variable valve timing control apparatus, the first and second protrusion portions are formed at the partition portions, and also corresponding recess portions may be formed at the side walls of the fluid chambers so that the protrusion portions are fitted to the recess portions, which may lead to complicated configurations of the driving-side rotation member and the driven-side rotation member. In addition, because a contact area between the bolt in a bar form and the protrusion portion is relatively small, a contact portion of the protrusion portion relative to the bolt may be deformed and a tightening portion of the bolt may change or fluctuate by repeat contact between the bolt and the protrusion portion. The most retarded angle phase and the most advanced angle phase may still deviate from the respective phases that are specified beforehand.
Accordingly, in a case where each of the most retarded angle phase and the most advanced angle phase as a basis for controlling the relative rotation phase deviates or fluctuates, the relative rotation phase is not appropriately controlled.
A need thus exists for a variable valve timing control apparatus which is not susceptible to the drawback mentioned above.